Acoustic shield for a tool powered by a gas-operated motor



1965 R. A- w. CLARKE 3,202,239

ACOUSTIC SHIELD FOR A TOOL POWERED BY A GAS-OPERATED MOTOR Filed June 4,1964 2 Sheets-Sheet 1 I H l Aug. 1965 R. A. w. CLARKE 3,202,239

ACOUSTIC SHIELD FOR A TOOL POWERED BY A GAS-OPERATED MOTOR Filed June 4,1964 2 Sheets-Sheet 2 29 l l f 3 QJJ 28 32 -26 Q 35 2 fj 38 36 l L/ 24 T37 25 l 25 5] 57 48 I I 50 49 I I -27 22-t I I 44 ML United StatesPatent 3,202,239 ACOUSTEC SHIELD FUR A TOOL POWERED BY A GAS-@PERATEDMOTOR Ronald Albert William larke, 21 Raymond Road,

London SW. 19, England Filed June 4, 1964, Ser. No. 372,470

Claims priority, application Great Britain, June 10, 1963,

23,032/63; July 12, 1963, 27,759/ 63 9 Claims. (Cl. 181--36) Thisinvention relates to an acoustic shield for a tool powered by agas-operated motor and of the type having an axially elongated bodycontaining the motor, exhaust outlet means arranged to discharge exhaustgas laterally from the body, and a working member which extends from oneend of the body and is axially movable relative to the body, the memberbeing actuated by the motor.

The present invention includes an acoustic shield for a tool powered bya gas-operated motor and of the type set forth, comprisingan elongatedcasing lined with a sound-absorbing material and shaped so as at leastpartly to surround the body of the tool when fitted thereto and toprovide between the body of the tool and an inner surface of the liningof the casing a passage which is open to atmosphere and is ofcross-sectional area at least as great as that of the exhaust outletmeans, the casing being adapt-ed to be fitted to the tool relatively tothe exhaust outlet means so that the exhaust gas flows through thepassage.

The invention will now be described, by way of example, with referenceto the accompanying somewhat diagrammatic drawings, in which:

FIGURE 1 is a longitudinal cross-section through a pneumatic drillfitted with an acoustic shield according to the invention, parts of thedrill of no relevance to the invention being omitted in the interests ofclarity; and

FIGURE 2 is a fragmentary longitudinal cross-section taken at rightangles to FIGURE 1.

Referring first to FIGURE 1, the drill has an elongated body 10 at thetop of which is a handle 11, operating trigger 12, and a coupling 13 bywhich a compressed air line can be connected to the drill. Within body10 is formed a cylinder 14, at the upper end of which is an advanceinlet port 15, at the lower end of which is a return inlet port 16, andwhich has between the advance port and the return port an exhaust outletport 17. Exhaust port 17 opens into an exhaust outlet 18 which projectslaterally from body 10 and is angled so as to direct air exhausting fromchamber 14 outwardly from the body and downwardly away from handle 11.

A piston 19 is provided within chamber 14 which reciprocates therein onthe admission of compressed air alternately to opposite ends of chamber-14 through advance port 15 and return port 16 respectively, passage ofair through ports 15 and 16 being controlled by a valve mechanismactuated by movement of the piston 19, which mechanism is conventionaland is therefore not illustrated. Cylinder 14, piston 19 and the portsand valve mechanism constitute an air-operated motor of the drill.

An anvil 20 is provided within body 10 so as to be struck by piston 19at the end of each advance of the piston and transmit the blow to achisel 21 which projects from the lower part or front head 22 of body 10and can be moved axially thereof. At the bottom of the body is a springloaded latch 23 which limits axial movement of chisel 21 and can beoperated to permit chisel 21 to be withdrawn for replacement.

Front head 22 is connected to the upper part of the body by bolts 24 onwhich are engaged respective nuts 25. Each bolt 24 passes through ahelical compression spring which biases the front head into engagementwith the lower part of the body. The maximum cross-sectional dimensionof body 19 is about 5 inches.

When the drill is in use so that reciprocation of the piston causes thechisel to strike a succession of rapid blows on the hard surface beingdrilled, the familiar noise of a pneumatic drill arises. A large part ofthe noise is due to the rapid expansion and frequency of pulses ofexhaust air. Another important cause of noise is vibration of thechisel, which is a member made of high-tensile steel and so emits ahigh-pitched ringing note. Noise results also from the impact of movingparts of the drill and from the chisel striking the surface beingdrilled.

An acoustic shield for this drill consists of two parts, a noiseconverter 26 and a vibration reducer 27. Noise converter 26 comprises ametal tube 28 of about 9 inches diameter and 12 inches length which hasan internal lining about 1 inch thick of sound absorbing material.Lining 29 is suitably made of a pressure felted hair felt having adensity of about 30 lbs. per cubic foot, but other materials could beused as will be described.

At its upper end tube 28 is outwardly rolled to provide rim 30 and isprovided with an inwardly extending annular flange 31 which constitutesa retaining stop for lining 29 when this is inserted in tube 28. Lining29 is held in position by internal bands 32 which are a press fit Withinthe lining. At the lower end of the tube 28 is provided a stepped tubehaving an outer cylindrical portion 33 which is welded to tube 2 8 andan inner cylindrical portion 34 which serves to hold lining 29 inposition, portions 33 and 34 being joined by an annular portion 33a ofwidth little more than the thickness of lining 29.

At diametrically opposed locations of annular portion 33a respectivelugs 35 are secured to flange 33 each by three bolts such as bolt 36,shown in FIGURE 2. Between each bolt 36 and portion 33a is a rubbervibration mounting 37. Lugs 35 extend inwardly from portion 33a and areformed each with a slot 38' which fits about one of the front head bolts24 and is secured thereto by one of the nuts 25. Noise converter 26 isthus fitted to the drill so as to surround body 10 and extend therealongto a location above exhaust outlet 18 and below coupling 13 so that airexhausted through outlet 18 is discharged into casing 26.

A passage 38 is formed between body 10 and lining 29, the lower end 39of passage 38, towards which end exhaust air is directed being open. Theupper end of passage 38 is closed by a rubber annular plate 40 the outerperiphery of which is provided with a skirt 41 which embraces tube 28,skirt 41 being pressed over rolled rim 30. Plate 40 has a centralthickened portion 42 which presses against the interior of lining 29 tokeep the lining in place. The interior periphery of annular plate 40 isshaped complementarily to the exterior of body 10 at the locationbetween exhaust outlet 18 and coupling 13 where plate 40 embraces body10, and forms an air seal with the body at that location.

A slit 43 extends from the outer periphery of the plate to the innerperiphery thereof, to permit the parts of the plate on opposite sides ofthe slit to be twisted apart so the plate can be fitted around the bodyof the drill. When plate 40 is fitted to the drill the inner edge offlange 31 presses into mutual contact the parts of plate 40 which lie onopposite sides of slit 43.

When the drill is in use, exhaust air discharged from outlet 18 isdirected through passage 38 to the'open end 39 and, passage 38 having across-sectional area much greater than that of exhaust outlet 18, theair can expand freely Within passage 38 so that the efliciency of theairoperated motor is not significantly, if at all, impaired. Some of theenergy of the expanding air is absorbed by so lining 29, thus partlysilencing the drill, while a large part of the high frequency noiseproduced around the body of the drill is converted to lower-frequencynoise.

It will be appreciated that specific dimensions and shapes of casing 28and specific lining materials can be selected according to thecharacteristics of the drill to be fitted with the acoustic shield ofthe invention. For example, the casing may only partly surround thedrill if the drill has a single exhaust outlet, and the size of thepassage between the body of the drill and the lining of the casing maybe varied provided the flow of air through the passage or through thepassage and the lining is not so retrictedas to produce any significantback-pressure in the cylinder. For use with a tool powered by aninternal combustion engine, the lining may be a steel mesh resistant toattack by exhaust gases, the manufacturers of such mesh commonly statingthe sound-absorptioncoefiicient of their material for a given angleofincidence. The casing described or a similar casing one inch longercan be fitted to most makes of pneumatic drill, road breaker, hammer andlike tools with good results, the arrangements of the majority of thesetools being similar.

Vibration reducer 27 is a resilient tubular gaiter' which comprises aflexible cylindrical rubber tube 44 one end of which is formed with aninwardly extending convoluted wall 45 provided with a centrally mountedboss 46. An aperture 47 extends axially through boss 46. Rubber tube 44surrounds the bottom of body It and the upper part of chisel21 whichprojects from the end of the body, and boss 46 embraces and grips chisel21. A rib 48 extends inwardly from the inner surface of tube 44 near theother end thereof, and engages a complementary chamber for reception ofexhaust gas from the outlet means, the improvement in said shield inwhich the shield comprises a rigid outer casing and a lining ofsound-absorbent material on the inside wall of the casing, the liningco-operating with the body of the tool to form an axially extendingpassageway which is open to the atmosphere at one end thereof so thatexhaust gas can pass freely through and out of said passageway;

2. A shield as claimed in claim 1, wherein the shield surrounds the bodyof the tool, and the passageway formed between the lining ofsound-absorbent material and th body is anannular passageway. t

3. A shield as claimed in claim 1, wherein the outer casing is a tubularmetal casing Within which is contained the lining, and having at the endof'the casing remote from the working member of the tool a sealingmember which fits about the body of the tool so as to close saidpassageway at the end thereof remote from the working member. I

4. An acoustic shield as claimed in claim 3, in which 'the sealingmember is a flexible annular plate having an outer periphery providedwith skirt means whereby the groove 49 formed in the outer edge of arubber sealing 7 ring 50 which surrounds the body of the drill. Ring 50has two holes 51 formed in its upper surface to receive the heads offront head bolts 24, and has a slit 52 whichextends from the inner tothe outer edge of ring d, so that parts of the ring on opposite sides ofslit 52 can be bent apart to permit ring 49 to be fitted about body 10.

When the drill is in use, vibration reducer 27 permits chisel 21 tomoveaxiallyof body without hindrance, but reduces the natural vibrationof chisel 21. Consequently the unpleasant ringing normally emitted by apneumatic drill is lessened.

Comparative instrumental analyses of the noise made by a pneumatic drillwhen fitted with an acoustic shield according to the invention and whenunshielded have shownthat when the drill is shielded there issubstantially less sound in the relatively high frequency bands of above300 cycles per second, the reduction being about 5 decibels in the300600 cycles/sec. band and in the bands above 4,800 cycles/secs, andapproximately 10 decibels in the bands from 600 to 4,800 cycles persecond. The loudness of the drill in the low frequency bands, below 300cycles per second, is not appreciably lessened, and

may even be slightly increased according to the construction of drill.However, because of the reduction of sound in the higher frequencies,the noise of the drill is made less disagreeable to the human ear, andthe level of in terference with speech is lowered by as much asdecibels.

In a practical test, it has been found that when a pneumatic drill isfitted with an acoustic shield according to the invention, the noise ofthe drill does not seriously impede a telephone conversation within aroom near the drill, whereas the same drill without the shield makes atelephone conversation impossible under the same conditions.

I claim:

1. In the known combination of a drill, hammer or like 7 tool having an,axially elongated body, a working member which extends from one end ofthe body and can be reciprocated axially of the body, and a gas-drivenmotor within the body operable to impart repeated impact blows to theworking member, the body being formed to provide shaped complementarilywith the exterior cross-section of the body of the tool, and formed witha slit which extends from the outer periphery to the inner periphery soas to permit the flexible plate to be fitted about the body.

5. In the known combination of (A) a drill, hammer or like tool having alongitudinally extending body, a gasoperated motor within the body, anda working member which extends from one'end'of the body and can bereciprocated longitudinally of the body by the motor so as to deliverblows to a Work surface, the body being formed to provide outlet meansthrough which exhaust gas from the motor is discharged laterally of thebody, together with (B) a rigid acoustic shield for the tool whichextends longitudinally of the body and fits thereabout so as to providebetween the shield and the body of the tool an is open at the endthereof adjacent the working mem ber, whereby exhaust gases flowing fromthe outlet means longitudinally through the passage can escape toatmosphere longitudinally through the open end,

'of the passage, and

(2) A lining of sound-absorbent material .within the.

shield, the lining being spaced from the body of the tool so as to leaveclear the annular passage between the body and the lining.

6. A shield as claimed in claim 5, wherein the soundabsorbent materialcomprises strands interlaced to provide air-filled interstices.

7. A shield as claimed in claim 5, in which the soundabsorbent materialis a pressure-felted hair felt.

8. A drill, hammer or like tool having an axially elongated body, aworking member which extends from one end of the body and can bereciprocated axially of the body, a gas-driven motor within the bodyoperable to impart repeated impact blows to the working member, the bodybeing formed to provide outlet means through which exhaust gas isdischarged laterally of the body, an acoustic shield comprising an outercasing mounted on the body and a lining of sound absorbent material onthe inside Wall of the'casing, the lining co-operating with the body ofthe tool to form an axially extending passageway which is open to theatmosphere at one end thereof so that exhaust gas can pass freelythrough and out of said passageway, and a resilient tubular gaiterfitted to the body of the tool adjacent the Working member thereof so asto extend from the body of the tool about the Working member, saidgaiter being secured to the working member so as to permit axialmovement of the working member but dampen the natural vibration thereof.

9. A drill, hammer or like tool as claimed in claim 8, in which thegaiter comprises a resilient tube having an inwardly extendingconvoluted wall at one end thereof, said wall having an apertured bosswhich engages firmly around the Working member, and an annular,less-resilient plate having an outer periphery connected to the otherend of the tube and an inner periphery engaging around 15 the body ofthe tool, the plate being formed with a slit which extends from theouter to the inner periphery as to permit the plate to be fitted to thebody.

References Cited by the Examiner UNITED STATES PATENTS 11/14 Manes181-36 4/29 Warhus 18156 8/38 Fuehrer 18l36 11/38 Pettit 181-36 8/58Wieczorek 18l-33 10/ 5 9 Kiekhaefer 181--3 3 8/60 Plummer 18136 4/ 62Leavell 181-36 FOREIGN PATENTS 2/ 62 Austria.

11/3 8 Great Britain.

3 50 Great Britain. 7/63 Great Britain. 5/3 3 Sweden.

LEO SMILOW, Primary Examiner.

1. IN THE KNOWN COMBINATION OF A DRILL, HAMMER OR LIKE TOOL HAVING ANAXIALLY ELONGATED BODY, A WORKING MEMBER WHICH EXTENDS FROM ONE END OFTHE BODY AND CAN BE RECIPROCATED AXIALLY OF THE BODY, AND A GAS-DRIVENMOTOR WITHIN THE BODY OPERABLE TO IMPART REPEATED IMPACT BLOWS TO THEWORKING MEMBER, THE BODY BEING FORMED TO PROVIDE OUTLET MEANS THROUGHWHICH EXHAUST GAS IS DISCHARGED LATERALLY OF THE BODY, TOGETHER WITH ANACOUSTIC SHIELD FOR THE TOOL WHICH IS FITTED TO THE BODY TO SURROUND ANDBE SPACED FROM A PORTION OF THE BODY INCLUDING THE PART OF